ML19235A122

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NRC MOV Training April 2019 Day 1 Part 1 Public Version
ML19235A122
Person / Time
Issue date: 08/23/2019
From: Michael Farnan, Thomas Scarbrough
NRC/NRR/DIRS/IRIB
To:
Thomas E, 415-6772, NRR/DIRS
References
Download: ML19235A122 (129)
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Text

Motor-Operated Valve Training Course Thomas G. Scarbrough Michael F. Farnan U.S. Nuclear Regulatory Commission PUBLIC VERSION NRC iLearn ID_372151 April 2019 Day 1 of 3

Agenda

  • Day 1
1. MOV Training Basis
2. MOV Training Objectives
3. MOV Design
4. MOV Lessons Learned
5. MOV Performance and Design Analysis 2

Agenda

  • Day 2
6. MOV Actuator Control Design
7. MOV Diagnostics
8. MOV Design-Basis Capability
9. MOV Preservice and Inservice Testing
10. MOV Inspection Issues
11. Operating Experience and Notices 3

Agenda

  • Day 3
12. NRC Inspection Procedures
13. Case Studies
14. MOV Inspection Recommendations
15. Sharepoint Web Site - Inspector Tools
16. Special Topic: 10 CFR 50.69
17. Roundtable and Q/A Session 4

Acronyms AC Alternating Current AF Application Factor AFW Auxiliary Feedwater AIT Augmented Inspection Team AOV Air-Operated Valve ASME American Society of Mechanical Engineers B&W Babcock & Wilcox BWR Boiling Water Reactor BWROG BWR Owners Group CCW Component Cooling Water CDF Core Damage Frequency COF Coefficient of Friction COL Combined License ComEd Commonwealth Edison CP Construction Permit CS Containment Spray CST Control Switch Trip CV Check Valve DC Direct Current DDGV Double Disc Gate Valve DP Differential Pressure DV Degraded Voltage ECW Essential Chilled Water Eff Efficiency EFW Emergency Feedwater EGM Enforcement Guidance Memorandum 5

Acronyms EPRI Electric Power Research Institute EQ Environmental Qualification FRG Federal Republic of Germany FRN Federal Register Notice FSAR Final Safety Analysis Report FT-LB Foot-pounds force FWG Flexible Wedge Gate GDC General Design Criterion GE General Electric GL Generic Letter GSI Generic Safety Issue HOV Hydraulic-Operated Valve HPCI High Pressure Coolant Injection HPCS High Pressure Core Spray HQ Headquarters HSSC High Safety Significant Component ICES INPO Consolidated Event System IDP Integrated Decision-making Panel IE Inspection and Enforcement IEEE Institute of Electrical and Electronics Engineers IMC Inspection Manual Chapter 6

Acronyms IN Information Notice INL Idaho National Laboratory INPO Institute of Nuclear Power Operations IP Inspection Procedure IR Inspection Report ISI Inservice Inspection IST Inservice Testing ITAAC Inspections, Tests, Analyses, and Acceptance Criteria JOG Joint Owners Group LER Licensee Event Report LERF Large Early Release Frequency LPCI Low Pressure Coolant Injection LRA Locked Rotor Amps LRC Locked Rotor Current LS Limit Switch LSB Load Sensitive Behavior LSSC Low Safety Significant Component MCC Motor Control Center MO Month MOV Motor-Operated Valve MOVATS MOV Analysis and Test System M&TE Measurement and Test Equipment MTR Material Test Report MUG MOV Users Group 7

Acronyms NEI Nuclear Energy Institute NPP Nuclear Power Plant NRC U.S. Nuclear Regulatory Commission NUGEQ Nuclear Utility Group on Equipment Qualification OAR Overall Actuator Ratio OD Operability Determination OE Operating Experience OM Operation and Maintenance OpESS Operating Experience Smart Sample P

System Pressure PAT Performance Assessment Testing PI&R Problem Identification &

Resolution PM Preventive Maintenance PMT Post-Maintenance Testing PPM Performance Prediction Methodology PL Pressure Locking PORV Power-Operated Relief Valve POV Power-Operated Valve PRA Probabilistic Risk Assessment PSI Pounds per square inch PSID PSI differential 8

Acronyms PWR Pressurized Water Reactor PWROG PWR Owners Group QA Quality Assurance QC Quality Control QME Qualification of Mechanical Equipment RCIC Reactor Core Isolation Cooling RCS Reactor Coolant System RFO Refueling Outage RG Regulatory Guide RHR Residual Heat Removal RIS Regulatory Issue Summary RM Radiation Monitoring ROL Rate of Loading RPM Revolutions Per Minute RTD Resistance Temperature Detector RTNSS Regulatory Treatment of Non-Safety Systems RWCU Reactor Water Clean-Up SDC Shutdown Cooling SE Safety Evaluation SER Safety Evaluation Report SF Stem Factor SFC Stem Friction Coefficient SIL Service Information Letter SONGS San Onofre Nuclear Generating Station SR Surveillance Requirement SRP Standard Review Plan SSC Structure, System, and Component STR Special Treatment Requirement TB Thermal Binding 9

Acronyms TOL Thermal Overload Relay TI Temporary Instruction TOL Thermal Overload TOR Thermal Overload Relay TPI Threads Per Inch TRF Torque Reaction Factor TS Torque Switch TSR Torque Switch Repeatability TST Torque Switch Trip TTC Torque Thrust Cell TU Technical Update TVA Tennessee Valley Authority UFSAR Updated Final Safety Analysis Report VAM Valve Actuator Motor VOTES Valve Operating and Test System VF Valve Factor YR Year 10

1. MOV Training Basis 11
  • In 1980s, significant MOV failures occurred that caused concerns for their capability to perform safety functions.
  • Based on MOV testing and research, numerous problems found with MOV performance and qualification.
  • Licensees expended significant resources to correct MOV issues.
  • NRC expended significant resources for MOV testing, evaluation, and inspections.
  • This training is intended to transfer historical and technical information on MOV design, operation, testing, and issues to NRC engineers and inspectors.

12

2. MOV Training Objectives 13

Describe design and operation of motor-operated valves (MOVs) used in nuclear power plants.

Describe regulatory requirements and guidance to provide reasonable assurance of capability of safety-related MOVs to perform safety functions.

Discuss specific MOV performance issues and lessons learned.

14

  • Discuss MOV inspection procedures.
  • Provide recommendations for MOV inspections.
  • Present tools for use by MOV engineers and inspectors.
  • Conduct roundtable discussion and Q/A session.

15

3. MOV Design 16

3.a Valve types and function 17

Anchor/Darling FWG Valve www.flowserve.com 18

MOV Gate Valve A

A GC99 0051 Electric motor Limitorque operator Yoke Disc Guide Seat ring A-A Valve stem Seat ring Disc 19 NUREG/CR-6611

Flexible Wedge Gate Valve 20

Anchor/Darling Flexwedge Gate Valve 21 FIGURE REDACTED

Wedge Gate Valve Tilting 22 FIGURE REDACTED

Valve damage from tipping 23 PHOTO REDACTED

Anchor/Darling Parallel Slide Gate Valve www.flowserve.com 24

Anchor/Darling Double Disc Gate Valve 25

Anchor/Darling Double Disc Gate Valve 26 FIGURE REDACTED

Anchor/Darling T-Pattern Globe Valve www.flowserve.com 27

Globe Valve 28

Anchor/Darling Y-Pattern Globe Valve www.flowserve.com 29

Valtek Ball Valve 30

Durco Plug Valve www.flowserve.com 31

Flowserve Ball Valve 32

NAF Butterfly Valve www.flowserve.com 33

Symmetric Disc Butterfly Valve 34

Double Offset Butterfly Valve 35

Triple Offset Butterfly Valve 36

3.b Motor actuator types and function 37

Limitorque SMB-0 38

39 Limitorque Nameplate PHOTO REDACTED

40 SMB-0 thru SMB-4 Exploded View FIGURE REDACTED

Limitorque Motor Operation GC99 0052 Sleeve bearings Stem nut Sleeve Belleville spring pack ACTUATOR OUTPUT TORQUE STEM THRUST STEM TORQUE SPRING COMPRESSION MOTOR TORQUE Torque switch Worm Valve stem Worm gear Spline Helical gear set 41

42 FIGURE REDACTED

43 FIGURE REDACTED

44 SMB-0 thru SMB-4 Power Train FIGURE REDACTED

45 Worm Gear Framatome website

46

47 Actuator Tripper Fingers PHOTO REDACTED

48 SMB-0 thru SMB-4 Tripper Finger FIGURE REDACTED

49 SMB-0 thru SMB-4 FIGURE REDACTED

50 SMB-0 thru SMB-4 Declutch Mechanism FIGURE REDACTED

51 SMB-0 thru SMB-4 Worm Shaft FIGURE REDACTED

Limitorque Torque Switch 52 FIGURE REDACTED

Limitorque Torque Switch Photograph 53 PHOTO REDACTED

Limitorque Torque Switch 54 FIGURE REDACTED

New Limitorque SMB/SB-000 Torque Switch 55 PHOTO REDACTED

Limitorque 2-Train Limit Switch 56 FIGURE REDACTED

Limitorque 4-Train Limit Switch 57 FIGURE REDACTED

58 Limitorque Limit Switch eBay

59 Limit Switch Contacts FIGURE REDACTED

60 Limit Switch Control Functions

61 SMB-00 & SMB-000

62 SMB-00 & SMB-000 Exploded View FIGURE REDACTED

63 SMB-00 & SMB-000 FIGURE REDACTED

64 SMB-00 & SMB-000 Tripper Finger Motor Mode FIGURE REDACTED

65 SMB-00 & SMB-000 Tripper Finger Manual Mode FIGURE REDACTED

66 SMB-00 & SMB-000 FIGURE REDACTED

67 SMB-00 & SMB-000 FIGURE REDACTED

68 SMB-00 & SMB-000 Manual Mode FIGURE REDACTED

69 SMB-00 & SMB-000 Drive Sleeve FIGURE REDACTED

70 Typical Blank Stem Nut & Stem Nut Lock Nut PHOTO REDACTED

71 SB Belleville Spring Compensator NRC Training E112

HBC-0 to 3 Operator 72 ISU Training Slide internet site

SMB-000/HBC Actuator 73 Can-Am Machinery

Limitorque Critical Parts List

  • Limitorque provides a list of critical parts for its actuators.
  • Stem nut is an example of a critical part in the Limitorque actuator.
  • Limitorque critical parts list is located on NRC Sharepoint site.

74

AC Motors

  • 3-phase 230/460/550/575 VAC Reliance squirrel-cage induction motors
  • Speeds: 900, 1800, 3600 rpm
  • Frame sizes: 48, 56, 180, 210, 256, 326
  • Factory lubricated sealed bearings
  • Output torque approximately proportional to square of per unit voltage.
  • Locked rotor torque is approximately 1.1 times starting torque.
  • For motor voltage less than 70% of rated voltage, actuator vendor should be consulted for motor performance.

75

DC Motors

  • 125/250 VDC Peerless compound-wound motors

- Compound-wound motors are compromise between shunt-wound (good speed regulation) and series-wound (high starting torque)

  • Output torque approximately linearly proportional to voltage.
  • Locked rotor torque is approximately 1.6 times starting torque.
  • For motor voltage less than 70% of rated voltage, actuator vendor should be consulted for motor performance.

76

Motor Insulation

  • Class B: 85 °C rise over 40 °C [mild 125 °C]
  • Class H: 135 °C rise over 40 °C [harsh 175 °C]
  • Class RH: 135 °C rise over 40 °C plus radiation

[very harsh 250 °C]

77

Motor Torque Output AC Motor Tqmotor = Tqrated (Vact / Vrat )2 Ftemp F app Tqmotor

= motor output torque Tqrated

= rated torque Vact = actual voltage Vrat = rated voltage Ftemp = factor due to motor heating Fapp = application factor DC motor Tq motor= Tqrated (Vact / Vrat ) Ftemp Fapp 78

Motor Definitions Duty Time during which a motor can carry its nameplate rating safely (Typically, 15 minutes for ac and 5 minutes for dc motors.)

Duty Cycle Number of strokes needed for intended service.

Available Duty Cycles Duty rating time divided by stroke time to determine number of strokes before exceeding duty rating.

Stroke Time Time to stroke valve in one direction (e.g., open to close).

Torque Control Control relies on torque switch trip (typically close direction).

Limit Control Control relies on limit switch trip (typically open direction).

79

Motor Definitions-Contd Motor RPM RPM listed on nameplate of motor is RPM of motor at running torque.

Running Torque Typically run rated at 20% of starting torque.

Starting Torque Motor torque at beginning of zero speed condition.

Locked Rotor Torque/Stall Torque Torque output of motor at zero speed and rated voltage and frequency noted on motor curve data sheet. If motor curve data sheet is unavailable, locked rotor torque is estimated to be 110% of start torque due to manufacturer designing motor with 10% margin to cover undervoltage conditions.

Motor temperature Motor temperature rise plus ambient temperature.

80

Limitorque Wiring Diagram 81 FIGURE REDACTED

AC Motor Curve 82 FIGURE REDACTED

DC Motor Curve 83 FIGURE REDACTED

Motor Actuator Environmental Qualification

  • Motor actuators undergo environmental qualification in accordance with IEEE standards, such as IEEE 323-1974, IEEE Standard for Qualifying Class 1E Equipment for Nuclear Power Generating Stations, accepted in RG 1.89 (Revision 1), and IEEE 382-2006, Standard for Qualification of Safety-Related Actuators for Nuclear Power Generating Stations, accepted in RG 1.73 (Revision 1).
  • Limitorque and EPRI have issued guidance for the environmental qualification of motor actuators.
  • As discussed later, ASME Standard QME-1-2007 references the IEEE standards as part of the equipment qualification requirements.

84

IEEE 1290-2015

  • REDACTED 85

86 IEEE 1290-2015 FIGURE REDACTED

87 IEEE 1290-2015 FIGURE REDACTED

88 IEEE 1290-2015 FIGURE REDACTED

IEEE 741-2007

  • REDACTED 89

Thermal Overload Relay (TOR)

Heater Selection

  • REDACTED 90

TOR Tripping Criteria

  • REDACTED 91

92 IEEE 741-2007 FIGURE REDACTED

93 IEEE 741-2007 FIGURE REDACTED

Limitorque Actuator Motor vs. Manual Mode

  • Actuators typically are not qualified for performing safety functions in the manual mode.
  • Actuators might not undergo qualification testing to demonstrate changes from manual to motor mode.
  • Some actuators have experienced problems with changing from manual to motor mode.
  • Licensees should ensure that actuators are returned to motor mode prior to declaring operable.

94

Limitorque Actuator Orientation

  • Limitorque actuators should be installed in preferred orientation to avoid performance issues.
  • Preferred orientation is motor, spring pack, and limit switch compartment in the same horizontal plane.
  • Other orientations might result in grease interfering with performance of motor, spring pack, or electrical components in limit switch compartment.
  • Licensees need to justify qualification of Limitorque actuators where installation will be inconsistent with preferred orientation.
  • If MOV cannot be installed in preferred orientation, licensee should conduct periodic inspections to identify any adverse impacts.

95

Rotork Actuator

  • 3-phase 220 VAC squirrel-cage induction motor
  • Electric motor-driven gear box similar to Limitorque
  • Oil gear lubrication
  • Open and close spring packs and switches
  • Motor shaft also acts as worm shaft
  • Nuclear Actuator Sizes 7NA, 11NA, 14NA, 16NA, 30NA, 40NA, 90NA
  • Syncroset watertight/explosion-proof actuators for containment
  • On September 6, 2018, Rotork announced that it is obsoleting its nuclear safety-related NA actuator with production ceasing by December 20, 2019.

96

Rotork Terminology

  • Syncroset (Nuclear): most electrical components remote
  • Syncropak (Non-nuclear): all electrical components on actuator
  • Insulation Sizes: Class B (125 °C), Class F (155 °C), and Class H (175 °C)
  • Nuclear Actuator Output Range:

- 7NA range: low rpm (25 ft lb) to high rpm (16 ft lb)

- 90 NA range: low rpm (1500 ft lb) to high rpm (540 ft lb) 97

98 Rotork NA Nuclear Electric Actuator Valve Magazine.com 10-21-2011

99 NRC MOV Course Manual

Rotork Operation

1. Motor operation initiated
2. Motor shaft (Wormshaft) rotates and turns Wormwheel
3. Wormwheel rotates Center Column
4. Center Column drives Drive Bush which turns to open and close valve
5. At full stroke, switch de-energizes motor control circuit
6. At high torque, Wormshaft overcomes Belleville spring and walks Wormwheel and actuates torque switch
7. In open direction, actuator has hammerblow before Center Column engaged 100

101 NRC MOV Course Manual

Rotork Actuator 102 PHOTO REDACTED

Rotork vs. Limitorque Actuators

1. Rotork uses modules instead of parts
2. Rotork Belleville washers installed behind motor
3. Rotork has only 1 gear arrangement (worm/wormwheel)
4. Rotork has a yoke for manual operation
5. Different bearing designs
6. Rotork NA actuators are watertight and explosion-proof
7. Rotork has 1 switch mechanism for torque and limit switches while Limitorque uses separate torque and limit switches 103

Rotork Operating Experience

  • REDACTED 104
4. MOV Lessons Learned 105

4.a Operating experience 106

MOV Operating Experience

  • NUREG-0660 included TMI-2 Accident Action Items II.E.4.2 (Containment) and II.E.6.1 (Valve Testing)
  • In 1980s, operating experience revealed weaknesses in design, qualification, maintenance, personnel training, and inservice testing (IST) for MOVs:

- Davis Besse Feedwater Failure (IN 85-50)

- Catawba Auxiliary Feedwater Failure (IN 89-61)

- Palisades PORV Block Valve Failure (AIT Nov. 1989)

  • Research programs by industry and NRC confirmed MOV design and qualification weaknesses.
  • NRC initiated regulatory action to address these weaknesses.

107

Past MOV Issues

  • Underestimation of required valve thrust or torque from assumptions for differential pressure (DP), valve factors, butterfly valve torque coefficients, and unwedging.
  • Overestimation of motor actuator thrust or torque output from assumptions for actuator efficiency, degraded voltage effects, ambient temperature effects, stem friction, and load sensitive behavior.
  • Potential unpredictability of valve performance under high flow conditions.
  • Significant variation in MOV performance.

108

Past MOV Issues (continued)

  • Deficiencies in MOV parts (e.g., torque and limit switches, motor shafts, pinion keys, valve yokes, and stem-disc connections).
  • Improper low voltage operation of motor brakes.
  • Inadequacies in some MOV diagnostic equipment in accurately measuring thrust and torque.
  • Gearbox and spring pack grease hardening.
  • Maintenance and training weaknesses.
  • Inadequate corrective action.
  • Motor thermal overload issues.

109

Regulatory Action

  • NRC Office of Nuclear Regulatory Research sponsored valve testing program by Idaho National Laboratory (INL).
  • Issued several Regulatory Issue Summaries and numerous Information Notices.
  • Performed reviews and inspections of MOV programs at nuclear power plants.
  • Updated Standard Review Plan and Inspection Procedures.

110

MOV Information Notices IN 1981-31, Failure of Safety Injection Valves to Operate Against DP IN 1985-20 and S1, Motor-Operated Valve Failures due to Hammering Effect IN 1985-22, Incorrect Installation of MOV Pinion Gear IN 1985-50, Complete Loss of Main and Auxiliary Feedwater at PWR Designed by B&W IN 1985-67, Valve Shaft to Actuator Key Failure IN 1986-02, Failure of Valve Operator Motor During Environmental Qualification Testing IN 1988-84, Defective MOV Motor Shaft Keys IN 1989-61, Failure of Borg-Warner Gate Valves to Close Against Differential Pressure IN 1990-21, Potential Failure of Motor-Operated Butterfly Valves IN 1990-37, Sheared MOV Pinion Keys IN 1990-40, Results of NRC-Sponsored MOV Testing 111

IN 1990-72, Testing of Parallel Disc Gate Valves in Europe IN 1992-17, NRC Inspections of MOV Programs IN 1992-23, Results of Validation Testing of MOV Diagnostic Equipment IN 1992-26, Pressure Locking of Motor-Operated Flexible Wedge Gate Valves IN 1992-27, Thermally Induced Accelerated Aging and Failure of ITE/Gould AC Relays IN 1992-59 (R1), Horizontally Installed Motor-Operated Gate Valves IN 1992-83, Thrust Limits for Limitorque Actuators IN 1993-74, High Temperatures Reduce AC Motor Output IN 1993-98, Motor Brakes on Actuator Motors IN 1994-10, MOV Motor Pinion Key Failure IN 1994-41, Problems with GE Type CR124 Overload Relay IN 1994-50, Failure of GE Contactors to Pull In at Required Voltage IN 1994-67, Pratt Butterfly Valve MOVs IN 1994-69, Potential Inadequacies in Torque Requirements and Output for Motor-Operated Butterfly Valves 112

IN 1995-14, Susceptibility of Containment Sump Valves to Pressure Locking IN 1995-18, Potential Pressure Locking of Gate Valves IN 1995-30, Low Pressure Coolant Injection and Core Spray Valve Pressure Locking IN 1996-08, Thermally Induced Pressure Locking of HPCI Valve IN 1996-30, Inaccuracy of Diagnostic Equipment for Motor-Operated Butterfly Valves IN 1996-48 and Supplement 1, MOV Performance Issues IN 1997-07, GL 89-10 Close-out Inspection Issues IN 1997-16, Preconditioning of Plant SSCs before ASME Code Inservice Testing or TS Surveillance Testing IN 2002-26 S2, Additional Flow-Induced Vibration Failures after a Recent Power Uprate IN 2003-15, Importance of Maintenance Follow-up Issues 113

IN 2005-23, Vibration-Induced Degradation of Butterfly Valves IN 2006-03, Motor Starter Failures due to Mechanical-Interlock Binding IN 2006-15, Vibration-Induced Degradation and Failure of Safety-Related Valves IN 2006-26, Failure of Magnesium Rotors in MOV Actuators IN 2006-29, Potential Common Cause Failure of MOVs as a result of Stem Nut Wear IN 2008-20, Failures of MOV Actuator Motors with Magnesium Alloy Rotors IN 2010-03, Failures of MOVs due to Degraded Stem Lubricant IN 2012-14, MOV Inoperable due to Stem-Disc Separation IN 2013-14, Potential Design Deficiency in MOV Control Circuitry IN 2017-03, Anchor/Darling Double Disc Gate Valve Wedge Pin and Stem-Disc Separation Failures 114

IN 1992-59, Revision 1 Horizontally Installed Motor-Operated Gate Valves

  • In October 1991, Crystal River determined that three EFW MOVs would not close during GL 89-10 DP testing.
  • In April 1992, FitzPatrick notified NRC that two double-disc MOVs might not fully seat during closure.
  • Horizontal installation can cause increased operating requirements and maintenance problems with spring pack, motor, and limit switch compartment at lowest actuator location.

115

Motor Hammering Effects

  • IN 1985-20 and Supplement 1 discussed MOV motor hammering effects, including mechanical overloading, motor overheating, starter contactor failure, circuit breaker trips, and valve seat jamming.
  • Hammering caused by spring pack energy reclosing torque switch contacts if worm gear is not self-locking.
  • IN 1993-98 reported that some motor brakes were not adequately sized to prevent hammering.
  • IN 2013-14 reported that MOV control circuitry modification used to avoid hammering might result in a dead zone if power interrupted during valve stroke.
  • Locking gear sets are recommended to prevent MOV motor hammering.

116

Related Information Notices

  • IN 2008-02, Findings Identified During Component Design Bases Inspections
  • IN 2012-06, Ineffective Use of Vendor Technical Recommendations
  • IN 2016-09, Recent Issues when using Reverse Engineering Techniques in Procurement
  • IN 2018-04, Operating Experience Regarding Failure of Operators to Trip Plant When Experiencing Unstable Conditions 117

Regulatory Issue Summaries

  • RIS 2000-03, Resolution of GSI 158: Performance of Safety-Related POVs Under Design Basis Conditions

Regulatory Issue Summaries

  • RIS 2015-08, Oversight of Counterfeit, Fraudulent, and Suspect Items in Nuclear Industry
  • RIS 2016-05, Embedded Digital Devices in Safety-Related Systems
  • RIS 2018-05, Supplier Oversight Issues Identified During Recent NRC Vendor Inspections 119

MOV Cheater Bars

  • MOV maintenance activities can be hazardous if not conducted according to procedure.
  • In January 2004, catastrophic MOV failure occurred at Crystal River Coal Plant with a fatal injury.
  • MOV was a 20 gate valve with an SMC-2 actuator.
  • On 1/22/2004, operators closed the MOV electrically and added manual force using a 24 long valve wrench to stop the valve from leaking.
  • Additional manual force was in the range of 190K to 260K lbs.

120

MOV Cheater Bars (continued)

  • On 1/29/2004, operators attempted to open MOV:

- 6 attempts to open electrically with 4 followed by driving valve in closed direction

- 3 attempts to open manually with wrench on last effort.

  • When valve came off seat, boiler water pressure acting over stem area generated a force ~ 26,000 lbs. into the housing.
  • Actuator failed and ejected pieces of the housing which struck the employee.
  • Analysis concluded that the manual closure on 1/22/2004 created multiple cracks in the housing.

121

122 Actuator Ejected Components FIGURE REDACTED

MOV Cheater Bars (continued)

  • Each motor closure on 1/29/2004 appears to have extended the cracks.
  • When valve came off seat, boiler pressure completed the cracking and ejected pieces.
  • Apparent cause

- Lack of training

- Plant personnel unaware that using a valve wrench could cause overtorque leading to housing failure

- Plant procedure not clear. Pull down interpreted to mean using valve wrench on handwheel to achieve good isolation

  • Limitorque issued Safety Bulletin 6-04 emphasizing proper use of maintenance procedures and prohibition of use of cheater bars.

123

Magnesium Rotor Degradation

  • Several MOVs with actuator motors manufactured with magnesium alloy rotors have failed.
  • Failures attributed to corrosion of magnesium alloy rotors.
  • Information Notices 1986-02, 2006-26, and 2008-20.

124

Motor Rotor Failure Experience

  • 1985 - issue discovered during EQ tests
  • Random motor failures have occurred since late 1980s
  • Additional motor failures reported in 2005, 2006, 2007 and 2008
  • Borescope inspections of motors initiated in 2007 by some licensees

- At least 17 motors replaced when last reviewed

  • Potential problem applicable to both BWR and PWR plants.

125

Rotor Background & Challenges Large percentage of MOV actuators are Limitorque design.

Limitorque actuators mainly use Reliance 3-phase motors.

Reliance motors designed with aluminum alloy or magnesium alloy rotors.

All size 48 and 56 frame motors are aluminum (2 to 40 ft-lb).

180 size frame (60 - 400 ft-lb) are magnesium (some exceptions).

Prior to 1995, Reliance did not maintain records on motor castings.

Simple visual inspection cannot discern aluminum vs. magnesium.

ASME testing and non-intrusive diagnostics have not been successful in determining internal rotor degradation.

Converting larger frame rotor to aluminum is not easy task.

Past preventive measures have not reduced failure rate.

126

Basic components of Induction AC motor 127

Rotor Construction 128

Rotor Construction Iron Lamination - Stator & Rotor Diagram with 3 laminations 129 PHOTOS REDACTED

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